Curing and pretannage of hides

ABSTRACT

HIDES MAY BE CURED AND PRETANNED BY: TREATING RAWHIDES WITH A SODIUM HYDROXIDE SOLUTION SO AS TO REACT THE LIPID MATERIAL IN ORDER TO CAUSE FORMATION OF SOAPS, LIMITED ATTACK ON PROTEIN MATERIAL PRESENT IN THE HIDES, AND SWELLING OF THE COLLAGEN IN THE HIDES; ADDING SODIUM CHLORIDE TO THE SODIUM HYDROXIDE SOLUTION IN ORDER TO ENABLE THIS SALT TO BE TAKEN UP FROM THE SOLUTION BY THE HIDES, CAUSING AN INCREASE IN THE STRENGTH OF THE SWOLLEN COLLAGEN; DEHAIRING THE HIDES; TREATING THE HIDES WITH SODIUM SULPHITE SOLUTION SO AS TO ADD STRENGTH TO THE SWOLLEN COLLAGEN; TREATING THE HIDES WITH A MIXTURE OF A QUATERNARY AMMONIUM SALT, AND A CALCIUM SALT IN ORDER TO PRECIPITATE ANY SOAPS PRESENT AND TO PLACE THE AMMONIUM SALT WITHIN THE REMAINING HIDE MATERIAL AND TO SEPARATE FASCIA TISSUE FROM THE REMAINING HIDE MATERIAL; AND PICKLLING THE HIDES WITH AN ACID SOLUTION SO AS TO EFFECT A SIZE REDUCTION AND STRENGTHENING OF THE SWOLLEN COLLAGEN. IF DESIRED, THE HIDES MAY BE BATED PRIOR TO BEING PICKLED. THE SO-CURED HIDES HAVE PROPERTIES WHICH ARE RELATED TO THE PROPERTIES OF AMMONIUM SALT. THE RESULTING HIDES CAN BE FURTHER TREATED IN ACCORDANCE WITH CONVENTIONAL TANNING PRACTICES.   D R A W I N G

nited States Patent 3,799,737 CURING AND PRETANNAGE 0F HIDES Don S.Elvrum, 6233 Saylin Lane, Annandale, Los Angeles, Calif. 90042 Originalapplication July 19, 1967, Ser. No. 654,432, now Patent No. 3,574,517,dated Apr. 13, 1971. Divided and this application July 2, 1970, Ser. No.52,017

Int. Cl. C142 1/02, l/06, 1/08 US. Cl. 8-94.16 9 Claims ABSTRACT OF THEDISCLOSURE Hides may be cured and pretanned by: treating rawhides with asodium hydroxide solution so as to react the lipid material in order tocause formation of soaps, limited attack on protein material present inthe hides, and swelling of the collagen in the hides; adding sodiumchloride to the sodium hydroxide solution in order to enable this saltto be taken up from the solution by the hides, causing an increase inthe strength of the swollen collagen; dehairing the hides; treating thehides with sodium sulphite solution so as to add strength to the swollencollagen; treating the hides with a mixture of a quaternary ammoniumsalt, and a calcium salt in order to precipitate any soaps present andto place the ammonium salt within the remaining hide material and toseparate fascia tissue from the remaining hide material; and picklingthe hides with an acid solution so as to effect a size reduction andstrengthening of the swollen collagen. If desired, the hides may bebated prior to being pickled. The so-cured hides have properties whichare related to the properties of the ammonium salt. The resulting hidescan be further treated in accordance with conventional tanningpractices.

This is a division of Ser. No. 654,432, filed July 19, 1967, now US.Pat. NO. 3,574,517, dated Apr. 13, 1971.

BACKGROUND OF THE INVENTION One of the oldest arts or sciences known tocivilization pertains to the curing and tanning of hides so as toconvert them to a condition in which they are stable. As this field hasbeen developed, it has been discovered that the curing and tanning ofhides involves extremely complex physical and chemical factors whicheven today are not considered to be completely understood. To a degree,the curing and tanning of hides remains a field which tends to be moreof an art than a science.

A hide on an animal such as a cow or steer is frequently considered toconsist of three layers: an ectodermal or outer layer; a mesodermal ormiddle layer; and an endodermal or inside layer. The ectoderma issometimes referred to as the epidermis of a hide. The endoderma carriesan adherent fascia layer of a hide. This fascia layer is a thintissue-like layer. The fatty tissues which are often found on the insideof a hide attached to the endoderma are normally referred to as adiposetissues. Although various other terms are at times applied to designateparts of a hide, these terms are used herein so as to avoid confusion.

Both the physical and chemical characteristics of the various layersindicated in the preceding are quite important in curing and tanninghides. To understand this invention, it is necessary to understandsomething of the interrelationship and nature of these characteristics.Upon examination of a rawhide, it is apparent that such a hide containsvarious hairs emplanted within the follicles which extend into theectodermal layer of a hide and occasionally to a degree into themesodermal layer. The endodermal layer in common hides is distinctlydifferent from the ectodermal and mesodermal layers, and re- "icesembles a white type ofparchment tissue. Both the fascia and adiposetissue on a normal rawhide are, of course, of the character of otherbody tissue, and have a different appearance from the hide materialproper.

Generally speaking all parts of the hide consist of two different typesof material. The first is protein material; the second is lipidmaterial. Other types of materials such as serums may be present in ahide. The protein material is normally classified as collagen andkeratin material. A third type of protein material is termed elastin andmay also be present to a degree in a hide, particularly in adiposetissue. In general, the elastin is a fibrous type of material present ina hide as connective tissue. Generally it can be recognized by ayellowish cast.

Keratin, on the other hand, is generally considered as the protein ofepithelial or outer tissue. Thus, the term keratin is generally appliedto the protein found in hair, horns, feathers, nails and the like. Suchkeratin protein on a hide proper frequently is of a scale-likeappearance. The collagen protein in a hide normally has a sort ofcoil-like physical structure appearing much like a bundle, and is thepredominant protein tissue in a hide, which is important in an ultimateleather product. The lipid material may be classified as fatty material;it is found to various extents throughout the entire protein structureof a hide.

The curing of a hide in a conventional process essentially involves theremoval of at least some of the lipid material, keratin material, andremoval of adipose and fascia material from the ectodermal andmesodermal layers of the hide. In other than the most conventionalcuring processes, it may be desirable to retain on the hide keratinmaterial such as hair, and the endodermal or fascia layer on the hideproper. The present invention is not primarily directed to suchspecialized curing processes. The curing of a hide normally involves thetreatment of a hide so that the collagen within such a hide is placed ina form which can be rendered stable and is usable. To a degree, suchstability and usability normally result from subsequent tanning andrelated leather treatment processes.

Conventional curing processes employed with hides normally include thesteps of (l) soaking in water or dilute alkaline solutions; (2)mechanically defleshing so as to remove adipose tissue; (3) soaking in alime solution so as to attack and loosen keratin; (4) removing keratinmaterial such as hair; (5) washing so as to delime; (6) bating so as toalter the chemical character of the collagen; and, an optional step (7)soaking in an acid so as to pickle the hide. A hide cured in this manneris normally treated by a conventional tanning process such as vegetable,mineral, oil or solvent processes so as to be tanned into leather.

These steps are all related to, or are an outgrowth of the physical andchemical character of hides. As such hides are obtained for processingthey are covered with all sorts of extraneous matter such as driedblood, dirt and the like. The initial soaking softens this type ofmaterial. It also may result in the hide unevenly taking up some water.The defleshing operation serves to remove:

much adipose tissue and some of the contaminants on the hide surfacethat have not been removed in the soaking operation. The soaking in alime solution which follows in conventional curing process is designedto aid in the removal of unwanted keratin.

Such removal is based upon the fact that different types of protein canbe chemically attacked in different manners, so as to break down thepeptide linkage. In the lime soaking process the peptide linkages in thekeratin are attacked. It is noted that this step does not normallycompletely remove the keratin from hides. It only loosens 3 and attacksthe keratin so as to facilitate removal of such keratin structures ashair during a subsequent operation.

An important facet of the present invention is related to a degree tothe so-called liming of hides in conventional curing process. The lipidswhich permeate all parts of a hide, although present to greater degreesin some parts of the hide than others, are not salvageable in the formof their by-products by soaking hides in a lime solution. This isbecause, to the extent that such lipids are attacked by lime so as toproduce fatty acid radicals, such radicals are precipitated in place inthe hide by the lime in the form of calcium soaps. It is considered thatany attack on lipids occurring during the liming is comparativelylimited.

The necessity of removing keratin material during a conventional curingprocess is easily understood. Normally, hairy leather is not desired.Such removal may be accomplished mechanically once the hair on a hidehas been loosened by the liming step. It is also known to accomplish itchemically through the use of known reagents which preferentially attackkeratin. The washing which follows dehairing in a conventional curingprocess prevents any carryover on the hides proper to the subsequenttreatment. Sometimes it is carried out using an acidic solution so as todecrease the alkalinity of the hide material.

The bating operation referred to in the preceding is essentially anoperation in which proteins remaining in the hide are to a degreechemically attacked so as to alter or vary the properties in the proteinin a final leather. The bating process in conventional hide curing maybe carried out in a number of ways using acids or various salts such asammonium chloride or ammonium sulphate and one or more enzymes. Suchenzymes are considered to tend to remove various degradation productsresulting from the earlier operations on the ectodermal and endodermallayer of hides, to modify and attack to a degree all proteins includingthe collagen and the elastin.

The final pickling operation frequently used in curing hides, to modifythe protein structure of the hide so as to give the remaining hidematerial which has been cured as indicated in the preceding a certaindegree of physical strength, is accomplished by regulating the pH of thehide protein so as to cause a variation in the swollen character of thistype of material.

All of these steps in conventional hide curing processes requirerelatively prolonged periods. It is well established that it takes asignificant time interval to cure a hide. Such a period isdisadvantageous economically, inasmuch as it requires that anappropriate hide treating plant be relatively large in order to processa given volume of hides. Conventional curing processes as indicated inthe preceding do not make any provision for the economic recovery offatty acids from lipids. Since such acids have a significant value it isreadily seen that this is disadvantageous. Further, conventional curingprocesses require mechanical operations such as defleshing and removingkeratin material. Such mechanical operations are not considered to bedesirable from an economic standpoint. Such mechanical operations mayresult in disadvantageous hide damage if not carefully carried out.

SUMMARY OF THE INVENTION A broad objective of the present invention isto provide a new and improved method of curing hides which eliminatesvarious disadvantages and limitations of prior methods such as arebriefly indicated in the preceding discussion. A more specific object ofthis invention is to provide a method of curing hides which enables ahide to be cured in a comparatively limited time period. This isconsidered to be very advantageous economically.

Another object of the present invention is to provide a method forcuring hides which permits the recovery of lipid by-products such asfatty acid radicals. This is also considered to be of significanteconomic importance.

Another object of this invention is to provide a method for curing hidesin which defieshing is essentially accomplished chemically. This isconsidered important from an economic standpoint because it eliminatesthe disadvantages and limitations of mechanical defleshing.

The present invention is not only directed to interrelated process stepshaving advantages as indicated in the preceding. These advantages are toa degree related to, and are to a degree secondary to the production ofgood cured hides. An object of the present invention is also to providesatisfactory cured hides capable of being further processed into leatherby conventional methods. The invention, however, goes further than this.An object of the present invention is to provide hides containing abacteriostatic and fungicidal agent which serves to protect the leatherresulting from such hides from attack by bacteria and fungi. This isquite important in connection with mildew and the like attack uponleather.

The aforegoing objects of this invention are achieved by a process whichpreferably involves the following steps: treating raw hides with analkali metal hydroxide so as to saponify lipid materials underconditions so that the hydroxide attacks the protein materials in thehides to only a limited extent and tends to cause swelling of thisprotein material, particularly the collagen; treating the hides with asalt solution so as to cause an increase in strength of the collagenmaterial; chemically dehairing the hides using agents which are known tobe efiective for this purpose; contacting the hides with a salt solutiontending to give strength to the protein material, especially thecollagen; treating the hides with a quaternary ammonium salt whichserves to physically separate remaining fascia and adipose tissuefragments from the hides proper while simultaneously penetrating theswollen hide material in such a manner as to remain to a degree withinthis material; and pickling the hides with an acid brine so as to reducethe size of the swollen material, particularly swollen collagen, and tostrengthen this material so that the hides can be handled safely infurther operations.

The hides resulting from this series of process steps can further betreated in accordance with conventional curing processes. In thepractice of the invention advantageous results can be achieved byemploying only certain of the process steps indicated in the precedingwithout other of these process steps, although the entire sequence ofsteps indicated is designed and intended to be used together because ofthe manner in which the protein material in hides resulting from any oneof these steps is conditioned for the next following step to be mosteffective. Thus, it is possible to obtain the advantageous result of therecovery of products from lipids by merely using the first step of theentire process indicated in the preceding. The hides resulting from thiscan be treated further or cured in other manners, as, for example, bybeing mechanically defleshed in accordance with conventional practiceafter being treated so as to lower their pH, although this is notconsidered advantageous. Similarly, a quarternary ammonium salt may beused in the removal of fascia or adipose tissue without employing allthe process steps indicated. Such a quaternary ammonium salt may also beplaced in a hide cured by other processes, as for example, by soaking anotherwise cured hide in a solution of this material so as to produce ahide having advantageous characteristics as indicated.

Because of the complex character of the invention and the field to whichit pertains, the invention is best more fully described by reference toa specific method of treating hides. Various other objects andadvantages of this invention will be apparent from a detailed study ofthe remainder of this specification and the appended claims.

DESCRIPTION OF THE DRAWlNG FIG. is a cross-sectional view of aconventional steer hide which is intended to illustrate the parts of thehide referred to in the following detailed description so that thisdescription may be understood readily;

FIG. 2 is a side elevational view, partially in section, of a preferredapparatus for carrying out the process of this invention;

FIG. 3 is a crss-sectional view taken at line 33 of FIG. 2; and

FIG. 4 is a diagrammatic flow sheet indicating the preferred series ofprocess steps described in the following detailed description.

DETAILED DESCRIPTION OF THE INVENTION As indicated in the precedingbrief summary, the first step in the preferred manner of carrying outthis invention involves saponifying the lipid material with an alkalimetal hydroxide under such conditions that the protein material presentwithin a hide is only attacked to a limited extent, and under suchconditions that the collagen protein material present within the hide ispreserved and is caused to swell so as to increase significantly inphysical dimension. These results require relatively careful andaccurate control of process conditions. It is desired in this step todegrade substantially all Of the lipid material so that the reactionproducts can be recovered without affecting the basic protein structureof the hide in such a manner as to affect detrimentally the ultimateproperties of leather created from the hide.

The significance of this first step is best considered with reference toFIG. 1 of the drawing. Here the ectodermal, mesodermal and endodermallayers of a hide are indicated in a generalized manner. It will be notedthat hairs extend from hair follicles in the ectodermal layer and theadipose tissue is attached to the endodermal layer in an irregularmanner. Although FIG. 1 does not indicate it, various amount of fleshmay be attached to the hide along with this adipose tissue. In an actualhide, the layers indicated are not sharply defined, but tend to blendinto one another in an irregular manner which depends upon many factors.

The hairs on the ectodermal layers are primarily keratin protein. Thisprotein is present in a somewhat scaly form. Some keratin may also bepresent on the surface of the ectoderma in a form of scaly typedeposits. In all of the dermal layers collagen protein is present,primarily in a physical structure which in some respects tends toresemble a tightly wound series of overlapped, crossed coil springs.Such springs tend to appear as ropes which are laid upon one anotherlike the fibers in a nonwoven fabric. This is particularly the case inthe mesodermal layer. In all of these dermal layers some elastin tissue,appearing in a yellow form, serves to interlock other materialstogether,

All of this structure is permeated to a degree with lipids. In effect,these lipids can be considered as a secondary material associated withthe protein compounds present in a hide. Because of this, in order torecover products from the lipids it is also necessary to permeate theentire protein structure of a hide. It is well known that lipids can besaponified by alkali metal hydroxides so that soaps andglycerins can berecovered. Such recovery is a matter of prime importance as to theeconomics of this invention. This is because such by-products havesignificant economic value.

Although the first step of the present invention is directed to therecovery of such by-products it is also di-' rected to hide treatment soas to make the hide take on a physical character which facilitatessubsequent steps of the process. This is best explained by referringagain to the nature of the collagen within a hide. As previouslyindicated such collagen has a coil-like physical structure somewhatresembling a coil spring. These individual collagen springs or bundlesare extremely complex from a chemical standpoint, and include a seriesof different protein compounds joined together in what is best described as a polymer type of structure, such a structure beinginterlocked with related structures. The various protein compoundscontain a large number of different acidic and basic groups. Thesegroups influence, if not determine, various reactions of the collagenmaterial.

Such material is frequently referred to as having an isoelectric point,and such an iso-electric point is frequently defined by pH. Strictlyspeaking, this is improper since pH refers to the log of the reciprocalof hydrogen ion concentration in a solution. Obviously a hide is asolid, not a solution in the usual sense of the term. Hence, pH is asomewhat misleading Way of expressing the iso-electric point ofcollagen. It is better to consider the iso-electric point of collagensas that condition of the collagen where structure are balanced in such amanner that the structure itself can be said to be as dense as it canbecome. That is,

collagen is at its iso-electric point when it occupies the minimumphysical dimension that it can occupy without breakdown of the materialitself,

From this it will be apparent that the physical dimension of collagenbundles can be altered. When hide material is placed within an acidic ora basic solution acidic or basic radicals are taken up in one manner oranother from the solution so as to be held by the basic proteinstructure of the collagen. As this occurs the collagen bundles will tendto expand, much in the manner in which a coil spring expands when itsends are pulled. In general the higher the concentration of the acidicor basic radicals placed in contact with hide collagen, the greater suchexpansion.

Such expansion is visibly noticeable in hide collagen. It is apparent asan increase in the thickness of the hide. Such increase in thicknessresulting from expansion of hide collagen is accompanied by adeterioration in the physical strength of the entire hide material,presumably because the collagen bundles are stretched or elongated insuch a manner that the physical interlocking between them is disturbed.This is in many ways analogous to the loss in physical strength ofcommon newspaper type inexpensive paper when the fibers within suchpaper swell as a result of contact with water.

The first step in the process is intended to bring about collagenswelling so as to make the interior of hide material more open so thatthe saponification carried out during this first step may gosubstantially to completion, removing substantially all of hide lipidmaterial, including such lipid material which is locked in place withinthe various dermal layers by the physical structure of the hidecollagen. Once a hide is opened up in this manner, various subsequenttreatment solutions gain access to the interior of these dermal layersso as to accomplish various objectives as hereinafter indicated. Suchopening up or swelling of the collagen materials in a hide also makes iteasier to remove the products of the saponification from the hidestructure.

The first step of the process can fortunately be carried out so that thesame reagent can be used both to cause saponrfication and so as tocause: collagen swelling. This reagent is, as previously indicated, analkali metal hydroxrde such as sodium hydroxide. This reagent alsoaccompl shes during this first step other effects which are beneficialto the entire treatment process. It is well known that protein materialcan be digested with such a hydrox- 1de so as to be degraded to variousdifferent degrees. The first step of the process is controlled so thatsuch degradation is apparently limited to attack all hair keratinwithout significant attack on other protein present such as ectodermalkeratin which is quite important to the grain of leather. If such attackis limited to hair keratin by proper control of this first step, thehair on a hide can be subsequently removed from it by a subsequent stepin the process with a minimum of difiiculty.

It will be apparent from the preceding that it is possible to completelydigest a hide during the first step of the process. This result, or anyresult reasonably approaching it is avoided by careful control ofreaction temperature, concentration and time during this first step.Such control also involves careful control of the amount of agitation ofthe treatment solution during the first step. It further involves abuffering type action achieved essentially as a bonus as a result ofusing unclean hides containing adipose tissue, dirt, straw, dried bloodand the like. All of these factors to a degree are considered to beinterrelated to what is believed to be a synergistic type actionachieved as a result of this saponification.

During the first step, it is considered that the temperature of the hidein the treatment solution should be maintained at from about 85 F. toabout 100 F. and preferably at from 90 F. to 95 F. At lower temperaturesthan this, the desired saponification reactions tend to be too slow forpractical purposes. At temperatures above about 100 F., the degradationreactions affecting hide proteins including keratin and collagen tend tobecome sufficiently pronounced so that hide material is apt to bedamaged. All of the various reactions considered are however influencedby the other factors indicated in the preceding paragraph.

The time required to accomplish this first step will vary depending uponthe nature of specific hides being treated. It is presently consideredthat this first step should be carried out for a period of from to 90minutes. In general the time should be sufficient so that the first stepis carried out for a time just under the time necessary for hidecollagen to tend to break up and go into solution. While this is alimiting factor it is preferred to relate the time required in thisfirst step not only to the hide collagen tending to go into solution,but also to the point where ectodermal keratin will tend to do the samething. The maximum time for any specific type of hide required with theprocess can within these limits be deterrnined by routineexperimentation.

The amount of time will of course depend upon the concentration of thetreatment solution during this first step. For the saponificationreactions to go on satisfactorily, it is considered that the alkalimetal concentration in the treatment solution must be at least thatnecessary for this solution to have a pH of at least 12. On the otherhand it is apparent that at hydroxyl ion concentrations of at least 12,attack on protein material such as hide keratin and collagen becomesquite pronounced. Such attack must be limited so that the hide is notphysically destroyed, and preferably so that the ectodermal keratinother than hair is not measurably destroyed. In general, however, thegreater the hydroxyl concentration during this step, the more rapid thesaponification.

Because of these factors, it is considered that the limiting factorduring this first step must be the degree in which control of thehydroxyl ions attack on hide protein material can be achieved throughthe use of a buffering type of action. When various contaminants of anorganic nature are present, during this first step, such contaminantstend to be preferentially attacked by a high hydroxyl ion concentrationin preference to hide protein.

In general, therefore, the more contaminants present the greater thealkali concentration permissible during this initial treatment step.There is, however, a limiting value. When the alkali metal hydroxideconcentration reaches a point at which the various contaminants presentdo not serve to control or to buffer the high hydroxyl content so thatattack on hide proteins such as collagen and ectodermal keratin otherthan hair is minimized the hydroxyl concentration is too high for use inthe process. Such attack on hide proteins must be minimized so as toavoid ultimate detrimental affects to leather produced from the hide.The maximum hydroxyl concentration which can be used is best determinedby routine experimentation since this concentration will vary dependingupon a number of factors such as the specific type of hide beingtreated, the amount and nature of the contaminants present and thetemperature at which the first step is carried out.

Such control of hydroxyl attack on hide protein thus depends upon anumber of factors which are interrelated to other factors in carryingout this first process step. As steer hides are normally obtained fromslaughtering operations these fresh flayed hides carry various differentmaterials such as are indicated in the preceding in an amount sufiicientso that an amount of sodium hydroxide of up to about 25 percent byweight of the flayed hide is the maximum amount which shouldsatisfactorily be used. This percentage by weight is, of course, relatedto the degree of dilution during the first process step. It is basedupon dilution with an amount of water equal to the weight of the hidebeing treated. It will be recognized that this concentration correspondsto a solution having a pH which is well above 12.

A surprising facet of the first step of the process is the role of thesoluble soaps formed as a result of the saponification reactions whichoccur with the lipids present. These soaps appear to cause a synergistictype of effect which aid in penetration of hide collagen by the hydroxylions present. Such penetration is thus facilitated by the reactionproducts of alkali metal hydroxide and lipids as the saponificationprogresses. This is considered to make it possible for substantially allof the lipid material trapped within the collagen bundles to besaponified within a minimum period before any undesired unnecessarydegradation of either collagen or ectodermal keratin occurs. This isconsidered to be quite important as far as the total results achieved ofthe process are concerned. It is of course related to the rate at whichthe collagen fibers or bundles swell during the initial treatment step.

Such swelling as indicated in the preceding tends to detrimentallyaffect the strength of the hide being treated. For this reason it ispreferred to add a quantity of sodium chloride to the solution beingused as the process step is being carried out. Such sodium chloridetends to act to a degree to depress the amount to which the collagenbundles Will swell during this first process step. This is and of itselfis considered to aid in the maintenance of sufiicient hide strength sothat there is no reasonable danger of hides being torn apart byhandling, motion or the like. It is considered that the sodium chloridein some manner enters the intricacies of the collagen fibers or bundlesso as to serve to link the various parts of these fibers or bundles insuch a manner as to add physical strength as a result of an action whichis other than the action of depressing collagen swelling.

The amount of the sodium chloride which should be added as indicated inthe preceding paragraph is best determined on a purely empirical basis.The amount should be sufficiently great so as to serve to preserve andincrease hide strength as much as possible, without any excess of thesodium chloride being used. It is presently preferred to use an amountof sodium chloride which is equal to about 10 percent by weight of theflayed hides being treated. It is considered that lower quantities canbe used with various types of hides, particularly when the processconditions are carefully controlled so as to minimize physical damage tothe hides. The results achieved through the use of this sodium chlorideare essentially matters of degree, and a minor variation in the amountof sodium chloride applied is not considered to be overly important.

This first step of the process is preferably carried out with the hideor hides being treated being subject to mild agitation. Such agitationtends to remove reaction products such as soluble soaps and glycerinefrom the hide material so as to present unreacted hydroxyl ions to hidesso that the desired saponification will occur. The agitation used duringthis step should preferably be a mild agitation since the swollen hidescreated during this first step are comparatively tender, and harsh orvigorous agitation will tend to disrupt the hide material once it hasbeen swollen. In a sense this can be compared again with wet newspapertype paper. A dry newspaper type paper poses greater strength than a wetnewspaper. If physical stresses and strain such as could be tolerated bysuch a sheet of dry paper are applied to such a sheet of paper when wetthe paper will tend to be broken up and disrupted. The general type ofconsideration is present during the treatment of a swollen hide of thisfirst process step, and during the subsequent steps of the process.

Although such agitation can be accomplished in a number of differentways, it is presently preferred to accomplish it using a rotatable drumapparatus as indicated in FIGS. 2 and 3 of the drawing. This apparatus10 has a smooth interior wall drum 12 enclosed by smooth end walls 14.It is supported upon shafts 16 and 18 which in turn are supported bytrunnions 20. One of the shafts 18 is hollow and is connected by asuitable conventional rotating joint 22 to a pipe 24 used to supplytreatment solution to the drum 12. Belts 26 contact the drum for thepurpose of rotating it in order to create agitation within it. Suchagitation is increased by the use of relatively small lifters 28 locatedequidistant from each other around the interior of the drum 12. Each ofthese lifters is preferably provided with a rounded end in order tominimize the chances of hide damage. The drum 12 is provided with a drumopening adapted to be closed by a door 30. This opening is used incharging the drum 12 and in removing material from it.

The dimensions of the interior of the drum 12 in the apparatus 10 can,of course, be varied considerably depending upon various circumstances.With drums of different dimensions different quantities of hides can betreated and different quantities of reactants will be used. Also themost advantageous speed of rotation of the drum will vary depending uponthe size. In experimental work on the process of this invention anapparatus such as the apparatus 10 was constructed in which the distancebetween the end walls 14 was six feet ten inches, in which the internaldiameter of the drum was seven feet four inches and in which each of thelifters shown extended from the drum interior six inches and was twoinches thick, and was provided with half inch radii rounded ends. Thesedimensions are considered to be important in reproducing the resultsachieved in one presently preferred manner of carrying out the processof this invention as hereinafter described.

In this presently preferred manner the first step of this invention wascarried out using an apparatus 10 constructed as previously described.The drum 12 was charged with sixteen fresh flayed steer hides, theexteriors of which were coated with the usual quantities of dung, driedblood, straw, dirt and other material usually on such hides as they comefrom a flay operation. No effort was made to specifically analyze theprecise types and quantities of such contaminants. The drum 12 was thencharged through the pipe 24 with an amount of water equal to the weightof the hides containing 10 percent by weight of the hides of sodiumhydroxide and 10 percent by weight of the hides of sodium chloride. Thesolution charged to the drum was at a temperature of about 95 F.although the solution could have been at other temperatures indicated.The drum was then rotated for twenty minutes at four revolutions perminute and then further rotated for ten minutes at seven revolutions perminute. At the end of this period the solution was drained from the drum12 and the liquid obtained was segregated for separate recovery of thematerials within it in accordance with known processes. At this pointthe drum was flooded with a hundred gallons of tap water and rotated forabout one minute at 25 revolutions per minute,

drained, flooded again with a hundred gallons of tap water and rotatedfor about one minute at 25 revolutions per minute and then drained.Although products could have 10 been recovered from these rinsesolutions they were discarded.

At this point the so-treated hides resulting from this first treatmentstep were ready for further treatment in accordance with this process.However, these hides can be treated in accordance with this process.However, these hides can be treated in other different manners thanhereinafter explained so as to produce cured hides or leather from thesehides. As an example of this, the hides after this first step may becontacted with a buffering solution such as calcium chloride solution soas to cause a shrinkage of the collagen bundles or fibers, reducing thehide thickness to essentially a thickness suitable for sole leathertannage. This treatment will of course add physical strength to the hidematerial since it causes a collapse of the collagen bundles or fibers,increasing the physical strength. The so-processed hide may then bedirectly treated with conventional practice as, for example, by knownprocesses of vegetable tanning so as to produce sole leather. Similarly,it would be possible to directly treat these hides in one or more othermanners involving steps conventional to the leather curing industry.

In the preferred manner of practicing the invention, the second step ofthe process involves removing hair keratin since such hair is notnormally desired on most leathers. If cured hides containing hair aredesired, this step can be omitted. Such removal is preferablyaccomplished chemically in the process because of the fact that thehides resulting from the first step are swollen and are relativelytender, and cannot withstand the physical handling for mechanicaldehairing without danger of damage to their physical structure. Thissecond step is preferably carried out utilizing conventional dehairingreagents for chemical dehairing under conventional conditions. A largenumber of such dehairing reagents are well known in the leatherindustry. Hence, no effort is made herein to specify such reagents.

In the preferred manner of practicing the invention hides described inthe preceding are left in the drum indicated and the drum is chargedwith a solution at about 70 F. containing an amount of water equal topercent of the initial hide weight and an amount of sodium sulfide equalto 2 percent of the initial hide weight. The drum is then rotated atseven revolutions per minute for a period of twenty minutes. During thisperiod the hair keratin is attacked and is removed from the hides.

Inasmuch as the pH of the solution used to accomplish such chemicaldehairing is significantly different from the pH of the solution used inthe first treatment step as the result of the second treatment stepthere will be a tendency for the degree of swelling of the hides tochange during the second step. In the method of practicing the stepindicated the hides will tend to shrink in thickness so as to decreaseroughly five to ten percent under their thickness as acquired during thefirst step. Such shrinkage tends to improve the strength of the collagenand grain keratin in the hides, but it also tends to compact thecollagen material within the hides so as to make the collagen fibers orbundles less permeable to the entry of reagents of the subsequent stepsof this process.

For this reason it is preferred to add to the solution used for chemicaldehairing further alkali metal hydroxide in order to contol hidethickness so that the collagen bundles or fibers are expanded to themaximum extent reasonably possible with hide strength. Also it ispreferred to contact the hides at this stage with additional sodiumchloride in order to maintain hide strength as much as reasonablypossible. Although such sodium hydroxide and sodium chloride may beadded along with the solution of a chemical dehairing agent it ispreferred to add the sodium hydroxide and sodium chloride as separatereagents after a certain degree of chemical attack on the hair keratinmaterial has transpired. It is also preferred to contact the hidesimmediately following the chemical dehairing with sodium sulphite so asto accomplish a fixative type of action serving to strengthen theexternal surfaces of the hide without appreciably changing the hidethickness.

The amounts of sodium hydroxide, sodium chloride and sodium sulphitewhich can be used in order to accomplish these objectives can be variedwithin comparatively wide limits. In general, sufficient sodiumhydroxide should either be added to the chemical dehairing solution orplaced in contact with the hide as a separate solution so as to get thehide thickness back to the thickness at the end of the first operationalstep in accordance with the process of this invention. This amount ofsodium hydroxide may be easily determined empirically. In suchdetermination it should also be taken into consideration that the sodiumhydroxide may tend to react with certain chemical dehairing solutions.The amount of sodium chloride used at this stage of the process of theinvention is also best determined empirically. The increase in hidestrength and the maintenance of hide strength through the use of sodiumchloride either at this or other process steps of this inventionessentially involve what may be referred to as a continuous variablesituation up to the point where the further addition of sodium chlorideserves no beneficial result.

The amount of sodium sulphite also involves what may be regarded as acontinuous variable situation. The sodium sulphite in some manner notcompletely understood serves to make the external surfaces of a hide acomparatively tough, firm type of structure. Thus, when the sodiumsulphite is used a hide becomes much like a laminate in which two rigidlayers incase a comparatively soft core. The sodium sulphite is used insuch a manner that the ectodermal keratin and the exposed surfacecollagen bundles are fixed or made more firm so as to make the hide moresusceptible to satisfactory treatment in the subsequent step of theprocess. If hides are left for too long a period or at too elevated atemperature in contact with the sulphite ion, it is considered that thisfixative action will tend to be manifested within a hide interior, andit is considered that this is a disadvantage. In general, anytemperature from room temperature up to about 90 F. can besatisfactorily employed at this stage. It is considered that in generalthe contact of the sodium sulphite should be from about ten to aboutthirty minutes, and that the solution placed in contact with the hideshould contain from about .1 to about percent by weight sodium sulphite.

In the preferred manner of practicing the invention at the end of thetwenty minute period specified in the preceding, an amount of sodiumhydroxide equal to 2 percent of the hide weight and an amount of sodiumchloride equal to 2 percent of the initial hide weight and an amount ofwater equal to the initial hide weight is added to the drum. The drum isthen rotated at seven revolutions per minute for additional period offifteen minutes. This time period can be varied considerably dependingupon the nature of the hair on the hides, and is best regulatedemperically. Then as the drum is still rotated an amount of sodiumsulphite equal to 0.2 percent by weight of the initial hide weight isadded. Rotation of the drum is continued at the same speed for a periodof fifteen minutes. The solution is then drained from the drum, thedrain is flooded with fifty gallons of tap water, rotated for about aminute at seven revolutions per minute and then drained. The so-rinsedhides are then ready for what is referred to as the third process stepof the invention.

This third process step is considered to be quite important and to marka significant advance in the art of curing and pretanning hides. In itfascia or adipose tissue on the ectodermal layer of the hides is removedwithout the usual mechanical operations. Further, a hide is impreg natedwith a quaternary ammonium compound which not only serves to makepossible the stripping of the fascia tissue, but which also enters ahide being treated so as to affect the ultimate, final properties ofthese hides. This treatment step is preferably carried out withrelatively mild agitation of the hides being treated so that suchagitation aids in stripping the fascia tissue as it is loosened due tothe reaction of the reagents used. During this step an empiricallydetermined amount of sodium chloride is preferably present so as to aidin maintenance of hide strength in order to prevent any tendency for thehides to physically be damaged to as great an extent as possible.

The solution used in this third step preferably contains a solublecalcium salt such as calcium chloride for the purpose of forminginsoluble soaps with any residual sodium soap remaining at or on thesurface of hide as a result of the initial process step. It will berecalled that this initial process step yields a swollen hide structurein which the swollen bundles of collagen are interlocked and arerelatively tender. Because of the chemical nature of such collagen andthe physical condition of it, it is substantially impossible to removefrom hides in the first process step, even by the rinsing operationsspecified and by such rinsing as occurs during the dehairing operation,all vestiges of the sodium soaps produced. These vestiges of sodium areconsidered quite important in this third process step. During this stepthe relative heavy metallic ions necessary to form insoluble soaps, andspecifically the calcium ion, tend to provide what may be considered asheavy soap molecules which tend to make the physical hide structureamenable to splitting off of the fascia tissue.

Such splitting is however only accomplished in the presence of aquaternary ammonium salt having unique surface active properties. It ispossible to utilize in the process of this invention such salts asn-alkyldimethylbenzylammoniumdichloroisocyanate in which the alkyl maybe an alkyl radical from C to C or a mixture thereof, thedichloro-isocyanurate salt of this compound,n-alkyldimethylbenzylammoniumdichloro-isocyanate, or thedichloroisocyanurate salt of the preceding compound. From this it willbe seen that all of the satisfactory quaternary ammonium salts used atthis step of the process are isocyanates or isocyanurates. All of thesecompounds are considered to not only possess desirable surface activecharacteristics, but in addition are considered to be goodbacteriostatic and fungicidal agents.

During this third process step, as insoluble calcium salts are formed insome incompletely understood manner, a quaternary ammonium compound asspecified appears to act essentially as a wedge or knife, separatingfascia or adipose tissue from the collagen material in the hide. Inother words the two types of reagents used together cooperate in someincompletely understood manner to separate the collagen bundles orfibers from the remaining tissue structure. It is considered that asthis occurs the calcium soaps somehow or other tend to weigh down theremaining tissue structures and the exposed surface of the collagenbundles in such a manner as to alter the normal physical bonds in a hideconnecting the tissue structure to the collagen, enabling the sufaceactive type of the quaternary salt to split these two types of animalmatter.

Such splitting is best aided or facilitated by comparatively minoragitation. This agitation is considered to aid in the separation of thefascia tissues by gradually pulling away such tissue away from hidecollagen, continuously exposing new areas of contact between the fasciatissue and the hide collagen for further splitting" action of thereagents employed.

This splitting action is also considered to be facilitated by anotheraspect of this third treatment step. Obviously a calcium chloridesolution is much less basic than the sodium hydroxide solution used inthis first treatment step. Because of this it will tend to cause thecollagen fibers or bundles in the hides to decrease in physicaldimension. Such a decrease in physical dimension obviously changes thephysical properties of the hides themselves, making them somewhat lesstender. As such shrinkage occurs on the surfaces of the hides it isaccompanied by a physical change in the character of the collagen fibersor bundles which is considered to aid in separating fascia or adiposetissue, making the action of the quaternary salt or salts used morepronounced and eifective. No such corresponding change is noted on thetissue, and this is considered to be beneficial in facilitating tissueremoval.

This third treatment step can conveniently be carried out at anytemperature from about room temperature to about 90 F., and with carefulcontrol to about 100 F. At higher temperatures chemical damage to thehide collagen is apt to occur; at lower temperatures the splitting isapt to be too slow for practical purposes. The times required duringthis third treatment step can similarly be varied. It is preferred thatthe time be carefully regulated so that the only calcium soaps formedare at or adjacent to the hide surfaces so as to preserve the characterof the hide material. Since penetration of solution within the interiorof the hide is a function of time, this can be con trolled by keepingthe duration of this third treatment step relatively short, preferablywithin the range of from ten to thirty mintues.

The formation of calcium soaps is also to a degree dependent upon theconcentration. Sufiicient calcium ions should be present to accomplishthe desired objectives, without any excess being used. Generallyspeaking the solution contacting the hides at this step should containfrom about to 12.5 percent by weight of calcium chloride. If it is moredilute than within this range calcium soaps are not formed sufiicientlyrapidly for the splitting to occur in a desired manner, and at higherconcentration than are specified there is a tendency to undesirably loadthe hide material with calcium ions.

The quantity of the quaternary ammonium salt used during this step canalso be varied within a comparatively wide limit. This salt, in itsaction, apparently involves continuous variable situations. Thetreatment solution used in this third step can contain as little asone-thousandth of a percent by weight of the quaternary ammonium salts,while amounts up to about 5 percent can be used. Inasmuch as nosignificant advantage is apparent from the use of such largerquantities, it is generally preferred to use as little of this salt aspossible.

It is preferred to have present within the solution for this thirdtreatment step a quantity of sodium chloride which will serve to aid themaintenance of hide strength. Such sodium chloride is not necessary.When it is used it should be used in an amount sufficient to maintainthe maximum halide strength that can be obtained through its use. Ingeneral, a sodium chloride concentration of from to 25 percent in thetreatment solution can be satisfactorily employed, althoughconcentrations within this range involve the use of more sodium chloridethan is normally considered necessary.

In the preferred manner of practicing the invention hides are left inthe treatment drum following the chemical dehairing. An aqueous solutionwas used containing five percent by weight calcium chloride, 10 percentby weight sodium chloride and .001 percent by weightn-alkyldimethylbenzylammonium dichloro isocyanurate in which the alkylradicals were a mixture of alkyl radicals from C to C The drum was thenrotated at seven revolutions per minute for fifteen minutes. At the endof this period the drum was drained, rinsed with fifty gallons of tapwater and then again drained.

The hides resulting from this treatment operation are susceptible ofbeing directly further used in the manufacture of leather. It ispreferred however to reduce the thickness of the collagen bundles orfibers within these hides to a reasonable extent so as to increase theirstrength and make them suitable for tannage without significant dangerof damage occurring to them by handling. This may be conveniently doneby contacting the hides with an acid solution so as to pickle the hides.If desired, such a solution may contain sodium chloride to helpmaintain,

at this step, hide strength. The acid concentration and times of contactwith the hides in this final step are not considered critical so long asthe acid used does not chemically attack the hide collagen and so longas the desired results are accomplished within a reasonable period. Itis considered that any conventionally used acid may be used in thispickling step.

In the preferred manner of practicing the invention the hides remainingin the drum from the defieshing step are contacted in the drum with asolution containing five percent by weight sulfuric acid and 15 percentby weight sodium chloride while the drum is rotated at seven revolutionsper minute for a period of thirty minutes. At the end of this time thehide collagen :is reduced significantly in thickness. The hides werethen ready for removal and tannage in accordance with conventionalpractice.

An interesting and surprising facet of the invention is the fact thatleather made from hide cured or pretanned as herein described possessesproperties which are related to the properties of the quaternaryammonium salt used. Because the salts specified are fungicides andbactericides, this leather is remarkably resistant to various types ofattack by ambient influences. This is considered to be particularlysignificant in the manufacture of leather for use in moist, humidtropical climates.

Those skilled in the art of the curing and pretanning of hides willrealize that the invention herein set forth has a number of verydistinct advantages, and that it is capable of being used in variousmanners. For this type of reason, this invention is to be considered asbeing limited solely by the appended claims forming a part of thisdisclosure.

What is claimed is:

1. In a process of treating a flayed hide, the following steps:

applying to the flayed hide a first solution at a temperature betweenapproximately F. and 100 F. for a period between approximately 15minutes and minutes, the first solution containing the followingingredients:

an alkali metal hydroxide to saponify lipids in the hide, the alkalimetal hydroxide having a concentration to provide a pH of at least 12and having up to approximately twenty-five percent (25%) by weight ofthe flayed hide,

a sodium salt to limit swelling of the collagen within the hide, thesodium salt having up to approximately ten percent (10%) by weight ofthe flayed hide;

applying to the flayed hide a second solution contain ing a calcium saltto cause shrinkage of the collagen within the hide; and

applying to the flayed hide at a temperature of approximately 70 F. fora period of approximately twenty (20) minutes a third solutioncontaining the following ingredients:

an alkali metal hydroxide to control hide thickness, the alkali metalhydroxide having approximately two percent (2%) by weight of the flayedhide,

a sodium salt to maintain hide strength, the sodium salt havingapproximately two percent (2%) by weight of the flayed hide, and

sodium sulfide for removing hair keratin, the sodium sulfide havingapproximately two percent (2%) by weight of the fiayed hide.

2. In the process set forth in claim 1, the alkali metal hydroxide inthe first solution constituting sodium hydroxide and the sodium salt inthe first solution constituting sodium chloride.

3. The process set forth in claim 1, the alkali metal hydroxide in thethird solution constituting sodium hydroxide and the sodium salt in thethird solution con stituting sodium chloride.

4. In the process set forth in claim 1, the salt in the second solutionconstituting calcium chloride and the 15 alkali metal hydroxide in thethird solution constituting sodium hydroxide and the salt in the thirdsolution constituting sodium chloride.

5. The process set forth in claim 1 wherein the amount of sodiumhydroxide in the third solution is suflicient to return the thickness ofthe hide to the thickness of the hide after the application of the firstsolution.

6. The process set forth in claim 1 wherein a solution of sodium sulfiteis applied to the hide, after the application of the third solution tothe hide, to strengthen the external surface of the hide.

7. The process set forth in claim 6 wherein the solution of sodiumsulfite contains between approximately 0.1% and by weight of sodiumsulfite and is applied to the hide for a time period between 10 and 30minutes at a temperature up to 90 F.

8. The process set forth in claim 5 wherein a solution of sodium sulfiteis applied to the hide, after the application of the third solution tothe hide, to strengthen the external surface of the hide.

16 9. The process set forth in claim 8 wherein the solution of sodiumsulfite contains between approximately 0.1% and 5% by weight of theflayed hide and is applied to the hide for a time period between 10 andminutes at a temperature up to F.

References Cited UNITED STATES PATENTS 3,421,832 1/1969 -Minklei 894.l63,415,610 12/1968 Dexter et al. 894.l6 1,859,417 5/1932 Wavra 894.l62,937,068 5/ 1960 Panepinto 894.l6 3,574,517 4/1971 Elvrum 894.l6

MAYER WEINBLATT, Primary Examiner H. WOLMAN, Assistant Examiner US. Cl.X.R.

